WO2017056154A1

WO2017056154A1 - Communication device and communication system

Info

Publication number: WO2017056154A1
Application number: PCT/JP2015/077322
Authority: WO
Inventors: 陽輔西潟
Original assignee: 三菱電機株式会社
Priority date: 2015-09-28
Filing date: 2015-09-28
Publication date: 2017-04-06

Abstract

A reception counter storage unit (19) splits reception counter values into an upper byte and lower bytes, and stores said reception counter values. The reception counter storage unit (19) stores a value shared by a plurality of transmission sources as the upper byte, and stores values corresponding to each of the plurality of transmission sources as the lower bytes. A message determination unit (16) determines whether a message (20) is to be accepted by comparing a frame counter value included in the message (20), with the reception counter value generated from the value of the upper byte stored by the reception counter storage unit (19), and the value of the lower byte which corresponds to the transmission source of the message (20), and which is stored by the reception counter storage unit (19).

Description

Communication apparatus and communication system

The present invention relates to a communication technique using a frame counter.

In the IEEE 802.15.4 standard used for sensor networks, a security method for replay attack is defined.
A replay attack is an attack in which an attacker reuses a message transmitted from a sender to a receiver and transmits the message to the receiver. When the password is transmitted from the sender to the receiver, the password is prevented from leaking by transmitting the encrypted password. However, by reusing the encrypted password, the attacker can impersonate the sender even if the password string is not leaked.

In the IEEE 802.15.4 standard, it is specified that replay attack is prevented as follows.
The communication device on the transmission side transmits the frame counter value included in the MAC frame. The transmission side communication device increments the frame counter value each time a MAC frame is transmitted.
Each time the receiving communication apparatus receives and accepts a MAC frame, it stores the frame counter value included in the accepted MAC frame. When the frame counter value included in the MAC frame is equal to or smaller than the stored frame counter value, the receiving communication device discards the received MAC frame.
In the replay attack, since the MAC frame is reused, the frame counter value becomes equal to or less than the frame counter value stored in the receiving communication apparatus. Therefore, the replay attack can be prevented by processing as described above.

A wireless multi-hop communication system may be constructed by applying the IEEE 802.15.4 standard. In a wireless multi-hop communication system, multicast transmission is used when a route used for communication is maintained and when a message is transmitted by simultaneous broadcast. When multicast transmission is used, each communication device receives MAC frames from a plurality of communication devices.
In order to apply the IEEE 802.15.4 standard security method, it is necessary to keep the frame counter value between communication devices that transmit and receive MAC frames.

Non-Patent Document 1 describes a configuration in which each communication device continues to manage frame counter values.

When receiving MAC frames from a plurality of communication devices, each communication device needs to continue to manage the frame counter value for each communication device that is the transmission source of the MAC frame. Therefore, the amount of memory necessary for storing the frame counter value increases.
An object of the present invention is to reduce the amount of memory required for storing a frame counter value.

The communication device according to the present invention is:
A reception counter value is divided into an upper byte and a lower byte, a value common to a plurality of transmission sources is stored for the upper byte, and a value is stored corresponding to each of the plurality of transmission sources for the lower byte. A counter storage unit;
A reception counter value generated from the value of the upper byte stored by the reception counter storage unit and the value of the lower byte stored by the reception counter storage unit corresponding to the transmission source of the message; And a message determination unit that determines whether to accept the message by comparing the frame counter value included in the message.

In the present invention, the reception counter value, which is the frame counter value stored in the communication device, is stored separately for the upper byte and the lower byte. In particular, for the upper byte, a value common to a plurality of transmission sources is stored. As a result, the amount of memory required to store the frame counter value can be reduced.

1 is a configuration diagram of a communication system 1 according to Embodiment 1. FIG. 1 is a configuration diagram of a communication device 10 according to Embodiment 1. FIG. FIG. 3 is a configuration diagram of a message 20 according to the first embodiment. Explanatory drawing of the transmission counter memory | storage part 18 which concerns on Embodiment 1. FIG. Explanatory drawing of the reception counter memory | storage part 19 which concerns on Embodiment 1. FIG. 6 is a flowchart showing transmission processing of a message 20 according to the first embodiment. 5 is a flowchart showing reception processing for a message 20 according to the first embodiment. The figure which shows the hardware structural example in case the function of the communication apparatus 10 is implement | achieved by software. The figure which shows the hardware structural example in case the function of the communication apparatus 10 is implement | achieved by hardware.

Embodiment 1 FIG.
*** Explanation of configuration ***
FIG. 1 is a configuration diagram of a communication system 1 according to the first embodiment.
The communication system 1 includes a plurality of communication devices 10. Each communication device 10 has the same configuration. Each communication device 10 transmits / receives a message 20 to / from another communication device 10 by wireless communication.
In FIG. 1, the communication system 1 includes the three communication devices 10. However, the communication system 1 may include any number of communication devices 10 as long as it is plural.

FIG. 2 is a configuration diagram of the communication apparatus 10 according to the first embodiment.
The communication device 10 includes an antenna 11, a wireless communication unit 12, a message generation unit 13, a message transmission unit 14, a message reception unit 15, a message determination unit 16, a change signal output unit 17, and a transmission counter storage unit. 18, a reception counter storage unit 19, a transmission counter control unit 181, and a reception counter control unit 191.

The antenna 11 is an antenna for wireless communication.

The wireless communication unit 12 transmits / receives a message 20 to / from another communication device 10 via the antenna 11.

The message generator 13 generates a message 20 that is a message 20 to be transmitted to another communication device 10 and includes a frame counter value 23.

The message transmission unit 14 transmits the message 20 generated by the message generation unit 13 via the wireless communication unit 12 and the antenna 11.
The message transmission unit 14 determines the transmission timing using a rule such as CSMA-CA, requests the wireless communication unit 12 to transmit the message 20 at the determined transmission timing, and transmits the message 20.
Note that CSMA-CA is an abbreviation for Carrier Sense Multiple Access-Collision Avidance. CSMA-CA is a rule used in a communication method in which a plurality of terminals share the same line, and is used as a data link layer communication protocol in IEEE 802.11, which is a wireless LAN communication standard. In CSMA-CA, it is confirmed that there is no other terminal that is trying to receive before starting communication, and if no other terminal is communicating, transmission is started and the other terminal is communicating. In this case, after the communication of the other terminal is completed, transmission is started after waiting for a certain time.

The message receiving unit 15 receives the message 20 including the frame counter value 23 transmitted by the other communication device 10 via the antenna 11 and the wireless communication unit 12.

The message determination unit 16 determines whether or not to accept the message 20 by determining whether or not the frame counter value 23 is valid.
The message determination unit 16 compares the reception counter value 40 stored in the reception counter storage unit 19 to be described later with the frame counter value 23 included in the message 20 received by the message reception unit 15, thereby obtaining the frame counter value 23. It is determined whether or not is valid.

The change signal output unit 17 outputs the change signal 50 at a timing synchronized with the other communication device 10. The change signal output unit 17 changes a transmission counter value 30 and a reception counter value 40 to be described later by outputting a change signal 50.
Here, the change signal output unit 17 holds the time, and outputs the change signal 50 when a preset time is reached. The time held by the change signal output unit 17 is synchronized with the other communication device 10 by the time information transmitted from the other communication device 10. The change signal output unit 17 may acquire time information from an external time source such as GPS, and synchronize the time with another communication device 10.

The transmission counter storage unit 18 stores a transmission counter value 30. The transmission counter value 30 is updated when the message 20 is transmitted by the message transmission unit 14 and when the change signal 50 is output by the change signal output unit 17.

The reception counter storage unit 19 stores a reception counter value 40. The reception counter value 40 is updated when it is determined that the message 20 is received by the message determination unit 16 and when the change signal 50 is output by the change signal output unit 17.

The transmission counter control unit 181 updates the transmission counter value 30 stored in the transmission counter storage unit 18 when the change signal 50 is output by the change signal output unit 17.

The reception counter control unit 191 updates the reception counter value 40 stored in the reception counter storage unit 19 when the change signal 50 is output by the change signal output unit 17.

FIG. 3 is a configuration diagram of the message 20 according to the first embodiment.
The message 20 includes a local destination 21, a local transmission source 22, a frame counter value 23, an MIC value 24, and transmission data 25. Note that MIC is an abbreviation for Message Integrity Check.
The local destination 21 is set with the MAC address of the destination communication device 10. The MAC address set as the local destination 21 may be a unicast address indicating the destination communication device 10 or a broadcast address.
The local transmission source 22 is set with the MAC address of the communication device 10 of the transmission source.
As the frame counter value 23, the transmission counter value 30 stored in the transmission counter storage unit 18 is set.
The MIC value 24 is a value for confirming that the message 20 has not been tampered with, and an encryption key and transmission data 25 shared in advance between the transmission source communication device 10 and the transmission destination communication device 10. It is a value generated from As a specific example, the MIC value 24 is a value calculated by inputting an encryption key and transmission data 25 into a hash function.
The transmission data 25 is data transmitted to the transmission destination.

Here, the message generation unit 13 encrypts the transmission data 25 by an encryption and message authentication method called AES-CCM * defined in the IEEE 802.15.4 standard. In AES-CCM *, by encrypting the transmission data 25, the MIC value 24 for the transmission data 25 is also calculated, and the MIC value 24 and the transmission data 25 are integrated into the encrypted data 26.

FIG. 4 is an explanatory diagram of the transmission counter storage unit 18 according to the first embodiment.
The transmission counter storage unit 18 stores the transmission counter value 30 separately into upper bytes 31 and lower bytes 32 according to the control of the message transmission unit 14 and the transmission counter control unit 181.

The transmission counter value 30 is changed by the message transmission unit 14 when the message 20 is transmitted by the message transmission unit 14. The transmission counter value 30 is changed by the transmission counter control unit 181 when the change signal 50 is output by the change signal output unit 17.
Here, the transmission counter value 30 is incremented by 1 to the value of the lower byte 32 by the transmission counter control unit 181 every time the message 20 is transmitted by the message transmission unit 14. Further, when the change signal 50 is output by the change signal output unit 17, the transmission counter value 30 is incremented by 1 to the value of the upper byte 31 by the transmission counter control unit 181, and the value of the lower byte 32 is 0. To be.

FIG. 5 is an explanatory diagram of the reception counter storage unit 19 according to the first embodiment.
The reception counter storage unit 19 stores the reception counter value 40 into upper bytes 41 and lower bytes 42 according to the control of the message determination unit 16 and the reception counter control unit 191.
In particular, the reception counter storage unit 19 stores a value common to the plurality of communication devices 10 for the upper byte 41 and stores a value corresponding to each of the plurality of communication devices 10 for the lower byte 42. Here, the reception counter storage unit 19 stores a lower byte 42 for each MAC address 43 of the communication device 10.

When the message determination unit 16 determines that the message 20 is received, the reception counter value 40 is set to the value of the lower byte 42 corresponding to the transmission source of the message 20 and the lower byte of the frame counter value 23 included in the message 20. The value is set by the message determination unit 16. The reception counter value 40 is changed by the reception counter control unit 191 when the change signal 50 is output by the change signal output unit 17.
Here, the reception counter value 40 is incremented by 1 to the value of the upper byte 41 by the reception counter control unit 191 when the change signal 50 is output by the change signal output unit 17. At this time, the value of the lower byte 42 is not changed.

In addition, the reception counter storage unit 19 stores a flag 44 and a key generation number 45 for each MAC address 43 of the communication device 10.

The flag 44 is used to determine whether or not the communication device 10 that has transmitted the message 20 has changed the transmission counter value 30 after the change signal 50 is transmitted. That is, due to the time synchronization error between the communication devices 10, the transmission counter value 10 is changed in the transmission side communication device 10 even though the transmission counter value 30 and the reception counter value 40 are changed in the reception side communication device 10. The case where 30 is not changed may occur. In this case, the flag 44 is used to correctly determine whether or not to accept the message 20.
The flag 44 is changed to On when the change signal 50 is output by the change signal output unit 17. The flag 44 is changed to Off when the message 20 after the upper byte 31 of the transmission counter value 30 is changed is received in the On state.

The key generation number 45 is a generation number of an encryption key used for calculating the MIC value 24 and encrypting the transmission data 25. The encryption key specified by the key generation number 45 is used. The key generation number 45 is updated regularly or when the key is lost, and the encryption key to be used is changed.
Here, the key generation number 45 is stored for each MAC address 43 of the communication device 10, but may be a value common to all the communication devices 10.

*** Explanation of operation ***
An operation of communication apparatus 10 according to Embodiment 1 will be described.
The operation of communication apparatus 10 according to Embodiment 1 corresponds to the communication method according to Embodiment 1. The operation of the communication device 10 according to the first embodiment corresponds to the communication program according to the first embodiment.

<Premise>
As a premise for transmission / reception of the message 20, the communication device 10 exchanges the transmission counter value 30 with the adjacent communication device 10. Here, the communication apparatus 10 exchanges the transmission counter value 30 by using MLE protocol defined by IETF. Note that IETF is an abbreviation for Internet Engineering Task Force. The IETF is an organization that formulates standardization of technologies used on the Internet. MLE is an abbreviation for Mesh Link Establishment. MLE protocol is a Challenge-Response type protocol.

Specifically, the communication apparatus 10 exchanges the transmission counter value 30 with the adjacent communication apparatus 10 using MLE protocol as follows.
(1) The communication device 10 on the transmission side generates a random number value, and transmits the generated random value to the communication device 10 on the reception side as Challenge.
(2) When receiving the Challenge, the communication device 10 on the receiving side generates a random value, and sets the generated random value as Challenge. Then, the communication device 10 on the reception side transmits Challenge, the transmission counter value 30, and the MIC value generated from the random value received as Challenge to the communication device 10 on the transmission side.
(3) The communication device 10 on the transmission side receives the Challenge, the transmission counter value 30, and the MIC value transmitted from the communication device 10 on the reception side, and verifies the MIC value. If the MIC value is valid, the communication device 10 on the transmission side sets the transmission counter value 30 received from the communication device 10 on the reception side as the reception counter value 40 of the communication device 10 on the reception side. In addition, the communication device 10 on the transmission side transmits the transmission counter value 30 to the communication device 10 on the reception side together with the MIC value generated from the random value received as Challenge.
(4) The reception side communication device 10 receives the transmission counter value 30 and the MIC value transmitted from the transmission side communication device 10, and verifies the MIC value. If the MIC value is valid, the communication device 10 on the reception side sets the transmission counter value 30 received from the communication device 10 on the transmission side as the reception counter value 40 of the communication device 10 on the transmission side.
As a result, the transmission counter value 30 is exchanged between the communication device 10 on the transmission side and the communication device 10 on the reception side.

<Transmission of message 20>
FIG. 6 is a flowchart showing transmission processing of the message 20 according to the first embodiment.
In the transmission information acquisition process of S11, the message generator 13 acquires the transmission data 25 and the MAC address of the transmission destination of the transmission data 25.

In the counter value reading process of S12, the message generation unit 13 reads the transmission counter value 30 from the transmission counter storage unit 18. Here, the message generator 13 reads the upper byte 31 and the lower byte 32 and concatenates the upper byte 31 and the lower byte 32 to obtain the transmission counter value 30.

In the encryption process of S13, the message generator 13 receives the transmission data 25 and the encryption key shared with the transmission destination of the transmission data 25, and encrypts the transmission data 25.
Here, the message generator 13 encrypts the transmission data 25 using AES-CCM *, and generates encrypted data 26 including the MIC value 24.

In the message generation process of S14, the message generation unit 13 sets the MAC address of the transmission destination acquired in S11 as the local destination 21, sets its own MAC address as the local transmission source 22, and sets the transmission counter value 30 acquired in S12. The frame counter value is 23. Then, the message generator 13 generates the message 20 using the encrypted data 26 calculated in S13 as data including the MIC value 24 and the transmission data 25.

In the message transmission process of S15, the message transmission unit 14 transmits the message 20 generated in S14 from the antenna 11 to the transmission destination via the wireless communication unit 12. Then, the message transmission unit 14 adds 1 to the value of the lower byte 32 of the transmission counter value 30 stored by the transmission counter storage unit 18.

<Reception of message 20>
FIG. 7 is a flowchart showing the reception process of the message 20 according to the first embodiment.
In the message reception process of S <b> 21, the message reception unit 15 receives the message 20 from the wireless communication unit 12 via the antenna 11.

In the flag confirmation process of S22, the message determination unit 16 reads the flag 44 for the communication device 10 of the transmission source indicated by the local transmission source 22 of the message 20 received in S21 from the reception counter storage unit 19. Then, the message determination unit 16 determines whether or not the read flag 44 is Off.
If the flag 44 is Off, that is, if the message 20 after the change of the upper byte 31 of the transmission counter value 30 has already been received from the transmission source communication device 10 (YES in S22), the message determination unit 16 To S23. On the other hand, if the flag 44 is On, that is, before the message 20 after the change of the upper byte 31 of the transmission counter value 30 is received from the communication device 10 of the transmission source (NO in S22), The process proceeds to S26.

In the first counter determination process of S23, the message determination unit 16 transmits the lower byte of the communication device 10 that is the transmission source indicated by the upper byte 41 and the local transmission source 22 of the message 20 received in S21 from the reception counter storage unit 19. Read byte 42. The message determination unit 16 combines the read upper byte 41 and lower byte 42 as a reception counter value 40. Then, the message determination unit 16 determines whether or not the frame counter value 23 of the message 20 received in S21 is larger than the reception counter value 40.
If the frame counter value 23 is larger than the reception counter value 40 (YES in S23), the message determination unit 16 advances the process to S24. On the other hand, when the frame counter value 23 is not larger than the reception counter value 40 (NO in S23), the message determination unit 16 advances the process to S32.

In the first decryption process of S24, the message determination unit 16 decrypts the encrypted data 26 of the message 20 received in S21 using the encryption key shared with the transmission source indicated by the local transmission source 22 of the message 20.

In the first decryption determination process of S25, the message determination unit 16 determines whether or not the decryption of the encrypted data 26 has succeeded. In AES-CCM *, if the encrypted data 26 is successfully decrypted, the MIC value 24 has been successfully verified.
If the decryption is successful (YES in S25), the message determination unit 16 advances the process to S31. On the other hand, if the decryption fails (NO in S25), the message determination unit 16 advances the process to S32.

In the second counter determination process of S26, the message determination unit 16 transmits the lower byte of the communication device 10 that is the transmission source indicated by the upper byte 41 and the local transmission source 22 of the message 20 received in S21 from the reception counter storage unit 19. Read byte 42. The message determination unit 16 adds the value obtained by subtracting 1 from the read upper byte 41 and the lower byte 42 to obtain the reception counter value 40. Then, the message determination unit 16 determines whether or not the frame counter value 23 of the message 20 received in S21 is larger than the reception counter value 40.
If the frame counter value 23 is larger than the reception counter value 40 (YES in S26), the message determination unit 16 advances the process to S27. On the other hand, when the frame counter value 23 is not larger than the reception counter value 40 (NO in S26), the message determination unit 16 advances the process to S32.

In the second decryption process of S27, the message determination unit 16 decrypts the encrypted data 26 of the message 20 received in S21 using the encryption key shared with the transmission source indicated by the local transmission source 22 of the message 20.

In the second decryption determination process of S28, the message determination unit 16 determines whether or not the decryption of the encrypted data 26 has succeeded.
If the decryption is successful (YES in S28), the message determination unit 16 advances the process to S29. On the other hand, when the decryption fails (NO in S28), the message determination unit 16 advances the process to S32.

In the change determination process in S29, the message determination unit 16 determines whether or not the upper byte of the frame counter value 23 of the message 20 received in S21 is the same as the upper byte 41 of the reception counter value 40. That is, the message determination unit 16 determines whether or not the upper byte of the frame counter value 23 is a value after the change.
If the upper byte is the same (YES in S29), the message determination unit 16 advances the process to S30. On the other hand, if the upper byte is different (NO in S29), the message determination unit 16 advances the process to S31.

In the flag update process of S30, the reception counter storage unit 19 updates the flag 44 for the communication device 10 of the transmission source indicated by the local transmission source 22 of the message 20 received in S21 to Off.

In the counter value update process in S31, the message determination unit 16 sets the lower byte of the frame counter value 23 of the message 20 received in S21 in the lower byte 42 of the reception counter value 40. That is, the message determination unit 16 overwrites the lower byte 42 of the frame counter value 23 of the message 20 received in S21 on the lower byte 42 of the reception counter value 40 stored in the reception counter storage unit 19.

In the first discard process of S32, the message determination unit 16 discards the message 20 received in S21.

Here, the process of S23 is executed when the message 20 after the change of the upper byte 31 of the transmission counter value 30 has already been received from the communication device 10 as the transmission source. Therefore, when the process of S23 is executed, the upper byte 31 of the communication device 10 that is the transmission source and the upper byte 41 of the communication device 10 that is the reception side match. The lower byte 42 of the communication device 10 on the receiving side is changed based on the frame counter value 23 included in the message 20 after the upper byte 31 is changed.
Accordingly, the message determination unit 16 simply compares the frame counter value 23 with the value obtained by combining the upper byte 41 and the lower byte 42 as the reception counter value 40. As a result, when a replay attack is performed, the frame counter value 23 becomes equal to or less than the reception counter value 40, so that the replay attack can be prevented. On the other hand, in the case of the message 20 to be received, the frame counter value 23 becomes larger than the reception counter value 40, so that the message 20 is not erroneously discarded. That is, it is possible to make a correct determination while preventing the replay attack and preventing the message 20 from being accidentally discarded.

The process of S26 is executed when the message 20 after the upper byte 31 of the transmission counter value 30 is changed is not received from the communication device 10 as the transmission source. Therefore, when the process of S26 is executed, in the communication apparatus 10 that is the transmission source, before the upper byte 31 of the transmission counter value 30 is changed and after the upper byte 31 of the transmission counter value 30 is changed. There are times when
Therefore, the message determination unit 16 compares the value obtained by subtracting 1 from the upper byte 41 and the lower byte 42 as the reception counter value 40 and compares it with the frame counter value 23.
When the upper byte 31 of the transmission counter value 30 is not changed in the transmission source communication device 10, 1 is subtracted from the upper byte 31 of the transmission source communication device 10 and the upper byte 41 of the reception side communication device 10. The value matches. Further, the lower byte 42 of the receiving communication device 10 is not changed when the upper byte 41 is changed, and remains in its original state. Therefore, by setting the value obtained by subtracting 1 from the upper byte 41 and the lower byte 42 as the reception counter value 40, the message 20 is erroneously discarded while preventing a replay attack as in the processing of S23. It is possible to make a correct judgment without any problems.
On the other hand, when the upper byte 31 of the transmission counter value 30 has been changed in the transmission source communication device 10, the upper byte 31 of the transmission source communication device 10 is the upper byte 41 of the reception side communication device 10. It becomes larger than the value obtained by subtracting 1 from. That is, the frame counter value 23 is larger than the reception counter value 40. Therefore, the message 20 is not discarded, and the message 20 is not accidentally discarded. In addition, since the message 20 after the upper byte 31 of the transmission counter value 30 is changed is not received, the replay attack using the message 20 after the upper byte 31 is changed is not performed.

Note that there is a possibility that the message 20 after the upper byte 31 of the transmission counter value 30 is changed is received before the communication device 10 changes the upper byte 41 of the reception counter value 40. In this case, the frame counter value 23 is larger than the reception counter value 40. Therefore, the message 20 is not discarded and the message 20 is not accidentally discarded.

*** Effects of Embodiment 1 ***
As described above, the communication device 10 according to the first embodiment stores the reception counter value 40 by dividing it into the upper byte 41 and the lower byte 42. In particular, for the upper byte 41, a value common to a plurality of transmission source communication devices 10 is stored. As a result, the communication device 10 according to the first embodiment does not need to store the upper byte 41 for each adjacent communication device 10, and can reduce the amount of memory necessary for storing the reception counter value 40.

Also, in the communication device 10 according to the first embodiment, the message determination unit 16 has already received the frame counter value 23 in which the value of the upper byte 31 has been changed from the communication device 10 that has transmitted the message 20 in S22. Determine whether. If the message has already been received, the message determination unit 16 uses the value of the upper byte 31 after the value has been changed in S23. If not, the message determination unit 16 has not changed the value in S26. Is used to determine whether to accept the message 20. As a result, the communication device 10 according to the first embodiment makes a correct determination that prevents the message 20 from being accidentally discarded while preventing a replay attack.

*** Other configurations ***
In the above description, the transmission counter value 30 including the upper byte 31 and the lower byte 32 is included in the message 20 as the frame counter value 23.
However, only the lower byte 32 may be included in the message 20 as the frame counter value 23. Thereby, the message 20 can be shortened and the consumption of communication resources can be reduced.
However, in this case, since the upper byte 31 is not included in the frame counter value 23, it cannot be determined whether the upper byte 41 is the same as the upper byte of the frame counter value 23 in S29 of FIG. Therefore, some lower bits of the upper byte 31 are included in the message 20, and in S29, some lower bits of the upper byte 41 and some lower bits of the upper byte 31 included in the message 20 are included. Compare if is the same.

In the above description, the transmission counter value 30 is exchanged as a premise for transmission / reception of the message 20.
However, instead of exchanging the transmission counter value 30, the transmission counter value 30 and the reception counter value 40 may be determined by synchronizing the times.
Specifically, the upper byte 31 and the upper byte 41 are set to 0 in the case of time T1 as a starting point, and 1 is added to the upper byte 31 and the upper byte 41 every time the first reference time elapses. Similarly, the lower byte 32 and the lower byte 42 are set to 0 in the case of the time T2 as a starting point, and 1 is added to the lower byte 32 and the lower byte 42 every time the second reference time elapses. Thereby, if the time is synchronized, the transmission counter value 30 and the reception counter value 40 can be synchronized.

In the above description, since AES-CCM * is adopted, it is possible to determine whether or not the MIC value 24 is valid by decrypting the encrypted data 26. However, when another method different from AES-CCM * is adopted, a process for determining whether or not the MIC value 24 is valid is required in addition to the process for decrypting the encrypted data 26.

Further, the upper byte 31 and the upper byte 41 have the same number of digits, and the lower byte 32 and the lower byte 42 have the same number of digits. The lower byte 32 and the lower byte 42 are not allowed to carry after reaching the maximum value. Therefore, it is necessary to prepare the number of digits necessary for the communication system 1 to be configured.

*** Explanation of hardware configuration example ***
Finally, a hardware configuration example of the communication device 10 will be described.
The communication device 10 is a computer.
The function of the communication device 10 can be realized by software or hardware.
FIG. 8 is a diagram illustrating a hardware configuration example in a case where the function of the communication device 10 is realized by software.
FIG. 9 is a diagram illustrating a hardware configuration example in a case where the function of the communication device 10 is realized by hardware.
Hereinafter, a hardware configuration example of the communication apparatus 10 will be described with reference to FIGS. 8 and 9.

** When the function of the communication device 10 is realized by software **
When the function of the communication device 10 is realized by software, the communication device 10 includes hardware such as a processor 901, an auxiliary storage device 902, a memory 903, a communication interface circuit 904, a modulation circuit 905, and an antenna 11, as shown in FIG. Wear.
The processor 901 is connected to other hardware via the signal line 910, and controls these other hardware. The communication interface circuit 904 is a circuit for transmitting and receiving the message 20 according to a predetermined protocol. The modulation circuit 905 is a circuit that performs modulation for transmitting the message 20 on a carrier wave. The antenna 11 is as described above.

The processor 901 is an IC that performs processing. IC is an abbreviation for Integrated Circuit.
Specifically, the processor 901 is a CPU, a DSP, or a GPU. CPU is an abbreviation for Central Processing Unit. DSP is an abbreviation for Digital Signal Processor. GPU is an abbreviation for Graphics Processing Unit.
Specifically, the auxiliary storage device 902 is a ROM, a flash memory, or an HDD. ROM is an abbreviation for Read Only Memory. HDD is an abbreviation for Hard Disk Drive.
Specifically, the memory 903 is a RAM. RAM is an abbreviation for Random Access Memory.
The transmission counter storage unit 18 and the reception counter storage unit 19 are realized by the auxiliary storage device 902 or the memory 903.

The auxiliary storage device 902 stores a program that realizes the functions of the wireless communication unit 12, the message generation unit 13, the message transmission unit 14, the message determination unit 16, and the change signal output unit 17. Hereinafter, the wireless communication unit 12, the message generation unit 13, the message transmission unit 14, the message determination unit 16, the change signal output unit 17, the transmission counter control unit 181, and the reception counter control unit 191 are collectively referred to as “ Part.
This program is loaded into the memory 903, read into the processor 901, and executed by the processor 901.
Further, the auxiliary storage device 902 stores an OS. OS is an abbreviation for Operating System. Then, at least a part of the OS is loaded into the memory 903, and the processor 901 executes a program that realizes the function of “unit” while executing the OS.
Although one processor 901 is illustrated in FIG. 8, the communication apparatus 10 may include a plurality of processors 901.
A plurality of processors 901 may execute a program for realizing the function of “unit” in cooperation with each other.
In addition, information, data, signal values, and variable values indicating the processing results of “unit” are stored in the memory 903, the auxiliary storage device 902, or a register or cache memory in the processor 901.
The program for realizing the function of “unit” may be stored in a portable storage medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk, a Blu-ray (registered trademark) disk, or a DVD.

** When the function of the communication device 10 is realized by hardware **
When the function of the communication device 10 is realized by hardware, the communication device 10 includes hardware such as a processing circuit 990, a communication interface circuit 904, a modulation circuit 905, and an antenna 11, as shown in FIG.
The processing circuit 990 is a dedicated electronic circuit that implements the functions of the “unit”, the transmission counter storage unit 18, and the reception counter storage unit 19.
The processing circuit 990 is assumed to be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, a logic IC, a GA, an ASIC, and an FPGA. GA is an abbreviation for Gate Array. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field-Programmable Gate Array.
The functions of “part”, transmission counter storage unit 18 and reception counter storage unit 19 may be realized by one processing circuit 990, or “part”, transmission counter storage unit 18 and reception counter storage unit 19 may be realized by being distributed to a plurality of processing circuits 990.

** When the function of the communication device 10 is realized by a combination of software and hardware **
Some functions of the communication device 10 may be realized by dedicated hardware, and other functions may be realized by software or a program.
That is, some functions of the communication device 10 are realized by the processing circuit 990 shown in FIG. 9, the remaining functions of the communication device 10 are realized by a program, and the processor 901 shown in FIG. 8 realizes the remaining functions. The program may be executed.

** Additional notes **
The processor 901, the auxiliary storage device 902, the memory 903, and the processing circuit 990 are collectively referred to as “processing circuitry”.
That is, regardless of whether the hardware configuration of the communication apparatus 10 is the hardware configuration of FIG. 8 or the hardware configuration of FIG. 9, the function of “unit” is realized by the processing circuitry.
In addition, “part” may be read as “process”, “procedure”, or “processing”.
Further, the function of “unit” may be realized by firmware.

1 communication system, 10 communication device, 11 antenna, 12 wireless communication unit, 13 message generation unit, 14 message transmission unit, 15 message reception unit, 16 message determination unit, 17 change signal output unit, 18 transmission counter storage unit, 19 reception Counter storage, 20 messages, 21 local destinations, 22 local transmission sources, 23 frame counter values, 24 MIC values, 25 transmission data, 26 encrypted data, 30 transmission counter values, 31 upper bytes, 32 lower bytes, 40 reception counter Value, 41 upper byte, 42 lower byte, 43 MAC address, 44 flag, 45 key generation number.

Claims

A reception counter value is divided into an upper byte and a lower byte, a value common to a plurality of transmission sources is stored for the upper byte, and a value is stored corresponding to each of the plurality of transmission sources for the lower byte. A counter storage unit;
A reception counter value generated from the value of the upper byte stored by the reception counter storage unit and the value of the lower byte stored by the reception counter storage unit corresponding to the transmission source of the message; A message determination unit that compares the frame counter value included in the message and determines whether or not to accept the message.
The reception counter value is a value of the lower byte of the frame counter value included in the message in the value of the lower byte corresponding to the transmission source of the message when the message determination unit determines to accept the message. The communication device according to claim 1, wherein
The reception counter value, when a change signal is output, the value of the upper byte is changed,
The message determination unit determines whether or not the frame counter value in which the value of the upper byte has been changed has already been received from the transmission source of the message, and if it has already been received, the value after the value has been changed 3. The method according to claim 1, wherein the value of the upper byte is used and if the message has not been received yet, the value of the upper byte before the value is changed is used to determine whether to accept the message. The communication device described.
The communication device further includes:
A transmission counter storage unit for storing a transmission counter value;
The communication apparatus according to claim 1, further comprising: a message transmission unit that transmits a message including the transmission counter value stored in the transmission counter storage unit as the frame counter value.
The transmission counter storage unit stores the transmission counter value divided into upper bytes and lower bytes,
The communication apparatus according to claim 4, wherein the value of the lower byte is changed when the message is transmitted by the message transmission unit.
The communication apparatus according to claim 4 or 5, wherein the value of the upper byte is changed when the change signal is output from the transmission counter value.
A communication system comprising a plurality of communication devices,
Each communication device
The reception counter value is divided into an upper byte and a lower byte, a value common to other communication devices is stored for the upper byte, and a value corresponding to each of the other communication devices is stored for the lower byte. A counter storage unit;
A reception counter value generated from the value of the upper byte stored by the reception counter storage unit and the value of the lower byte stored by the reception counter storage unit corresponding to the communication device that is the transmission source of the message; A message determination unit that compares a frame counter value included in the message to determine whether to accept the message.